Add protocol v5 support

[tzussman]

Valgrind added file descriptor leak information to its XML files, introducing a new XML protocol version. Support it.

https://sourceware.org/git/?p=valgrind.git;a=blob;f=docs/internals/xml-output-protocol5.txt

[paulfloyd]

Protocol 6 was added in May 2025. It is quite a big change, adding all of the various summaries to the XML output.